1. Field of the Invention
The present invention relates to a system and a method for canceling an echo, and in particular to a system and a method for canceling an echo wherein a plurality of independently and variably delayed adaptive algorithm blocks are selectively applied to a delayed feedback signal to generate a plurality of echo components in parallel, thereby effectively canceling the echo component from an input signal.
2. Description of the Related Art
As a wireless communication service progresses, a need for a wireless repeater for expanding a communication service to a radio frequency wave shadow area is increasing. However, in case of the wireless repeater, a portion of a repeated signal S(t) transmitted from a transmission antenna 19 is fed back through a receiving antenna 11 of the repeater 10 as an echo component e(t) because frequencies of a received signal r(t) and repeated signal S(t) are identical. Therefore, an oscillation of the repeater 10 occurs due to an amplification of the echo component e(t) within the repeater 10 as shown in FIG. 1.
In order to prevent the oscillation, an interference canceller system (ICS) repeater which cancels the echo component through a digital signal processing by subjecting the received signal to an intermediate frequency converter 13 and an analog-to-digital converter 14 is used. In order to cancel the echo component, an adaptive algorithm filter is generally used. Least mean squares (LMS), RLS, LSL and IIR filters are examples of the adaptive algorithm filter. However, the LMS filter which is stable and requires a small amount of calculation is widely used as the adaptive algorithm filter.
It is important to determine a number of filter taps sufficient for canceling the echo component when designing the adaptive filter. Theoretically, when the number of the filter taps is set to be more than a maximum delay time of the echo path, a complete cancellation of the echo component is possible. However, a structure of the adaptive filter becomes complex, an operation load increases and a signal distortion is increased due to a quantization noise generated in the adaptive filter where the echo component is small.